NEW YORK — Twitter's stock sank to an all-time low after a post-IPO lock-up period preventing employees and early investors from selling expired on Tuesday.

Lock-up periods prevent company insiders from selling stock following an initial public offering. CEO Dick Costolo and co-founders Jack Dorsey and Evan Williams have said that they had no plans to sell their stock when the lock-up expired, 180 days after Twitter's initial public offering.